Muscle guarding, and so on..

From a Facebook thread started by Taylor Sun, in Skeptical Massage Therapists group:

>> "I would love to foster a discussion around the idea of "muscle splinting" or "guarding" as a protective mechanism that the organism is engaged in due to perceived threat or repeated exposure.... Can we think of muscle splinting as one of these plastic-stimulus-responses that as manual/massage therapists we can interact with in a site-specific manner order to give the organism a new engram or encoding to work with?"

(What follows is my reply:)

"I think this is a great question. I have many thoughts on it.

"In no particular order:

1. I think "muscle" is an innocent victim, too often blamed for shenanigans the NS gets up to. As long as it's not frankly diseased, muscle is just being obedient to whatever it's told to do by NS motor output.

2. It makes sense to me that the spinal cord (along with its assorted intrinsic, or more rostral but bidirectional, nuclei) is a "first responder" to nociceptive input. It dangles out there into the "body" with all its array of PNS coming out of it and into it; it's the oldest part of the CNS so it has seniority. The rest of the CNS came along a lot later, with one of *its* big jobs being to inhibit spinal cord reflexive activity.

3. Nociception is a stimulus to the spinal cord which may or may not be processed at more rostral levels of CNS, but for sure, the spinal cord (plus the nuclei it came with) will notice it.

4. The spinal cord operates reflexively. Smooth muscle is contracted by the ANS (cell bodies in lateral horn) and striate muscle is contracted by lower motor neurons (cell bodies in anterior horn). In comes nociceptive input. There are lots of interneurons, glia, all sorts of things in the spinal cord extending many segments. All of them affect each other. They get excited over nociceptive input if not discouraged from doing so by descending inhibition.

5. A nociceptive input doesn't even have to reach the brain before it will be dealt with reflexively by the spinal cord. (E.g., touch a hot stove by accident and the hand jerks away before any sensation arrives to conscious awareness.)

6. Nociception is occurring constantly. But tonically, not phasically. The spinal cord actively deals with it all the time.

7. Our more rostral centres adapt easily to stressful inputs of any kind, as long as they are spaced, and not too intense. This is the way graded exposure works, when it works. The brain gets used to fleeting discomforts, weird positions, gait disturbances, whatever. These are defenses (mounted by the spinal cord, reflexively), not defects of structure (most of the time anyway). (Asymmetric resting positions, combined with external mental focus, are the two biggest contributing behavioural factors to nociceptive input that goes under the radar, IMO)

8. Anyway, spinal cord takes care of business, unless and until some of its striate motor or smooth motor or both at the same time output, pulls some other portion of the 72km/45 miles of peripheral neural array, or any of its connected vasculature, into "mechanical deformation". Then, oops! we have something that could act just like a tunnel syndrome.

9. The literature on tunnel syndromes all says the same thing: the sensory system will be affected first, and pain felt in a region that's neuroanatomically plausible (same as the new description for neuropathic pain) will be the predominant complaint.

10. So, an evolutionarily conserved strategy, reflexive tightening/contraction, deployed by the oldest bossiest part of the CNS, the spinal cord, which doesn't have much more hard drive than when fish invented it in the Devonian period 500 million years ago, which seemed reasonable at the time (if we were still fish maybe), has led to a situation where *more* nociception, stemming from somewhere else, occurs. (Bear in mind that the oldest parts of the NS have been dealing with it this way since the beginning of the NS, and nature never gets rid of anything that works.)

11. But eventually something's gotta give, and descending inhibition doesn't work automatically anymore. Nociception has become so tonic and from so many more afferent nerves, that glia have glee-a-fully arrived to augment the process, and the entire input becomes a positive physiological feedback loop. Central sensitization has tipped the NS into "every movement hurts".

12. If the NS is normal, and if associated vasculature is normal, the possibility exists that the NS can be hacked successfully so it can reboot. But the reboot has to happen from rostral areas, backward. Thank goodness for yes-ciceptive exteroception and fast dorsal columns, that can bypass all the flood waters and cars in the ditch within the dorsal horn, and get some new fresh regional info up to the brain so it can have something novel and pleasant to work with and make new body schema/representations from.

13. Non-specific FX and descending inhibition must be juiced up as much as possible. If the attached human brain knows what's going on, because the person in it has been successfully recruited to the effort and is willing to do their part, hacking such a NS can proceed in a clinically successful manner, i.e., improved ROM and decreased pain on movement. Then movement homework can take care of the physiological details over the next few days until peace prevails in the entire NS.

14. What I find quite fascinating is how little the CNS gives a fig about the "person" who has to ride around inside it, feeling/dealing with all the pain nonsense it can generate. Not entirely sure about this, but it seems to me that the bigger/more connected the brain, the more suffering its conscious awareness may have to endure when pain arises.

15. It pays, big time, to explore all the movement corners of one's own body, well in advance of any pain problem, so one can stave off most of it through simple movement hygiene. Especially, avoiding consistent asymmetric sleeping on one side only or other default resting positions, stances, leg-crossing, bag-carrying, etc., is a good investment of whatever "will power" one may possess, to avoid a world of dumb hurt.

16. Barring some frank disease, or being hit by a truck, simple movement awareness could keep most people, mostly out of pain-treatment offices like mine, most of the time. If everyone practiced Feldenkrais for example, most of us would be out of business."

.....

None of this answered the question, of course... But the question stimulated a bunch of thoughts that had been roiling around in my brain for a long time, and acted like a spigot for me to splash them out onto an existing thread. So, thank you Taylor.

Sept 22 2015: Text correction. I had the terms tonic and phasic backwards. Text reads correctly now.